Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in multi-color arrays that can be controlled to deliver virtually any color light, and contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting system, a light fixture, lighting unit, lamp, “light bulb” or more simply a “bulb,” which includes one or more power supplies to power the LEDs. An LED fixture may be made in the form of a fixture to be used in place of or instead of a standard incandescent or fluorescent fixture.
Light of varied color hues, or differing correlated color temperature (CCT) can be created by combining LEDs with different emission color points or “color bins.” These bins can vary somewhat and be adapted by using firmware to set drive current and therefore brightness. Typically, the lighting system is designed so that each color light source can be managed separately based on the drive current characteristics for that color. The power supply or “driver” is designed to match the configuration of LEDs in the lighting system so that precise control can be accomplished by using separate color control channels. With such an arrangement, a desired CCT can be maintained at any dimming level or user-configurable CCT can be provided. As one example, an LED lamp can be dimmed following the logarithmic profile of color vs. brightness exhibited by incandescent lamps. For some LED lighting products, there is a need to use an independent or pre-existing constant-current driver for the LEDs. With such a driver, the color control described above cannot be accomplished by independently addressing the current supplied by the driver to each color of LED.